1. Field of the Invention
Aspects of the present invention relate to an organic electrolyte solution including a vinyl-based compound and a lithium battery using the same, and more particularly, to an organic electrolyte solution including a vinyl-based compound which can suppress degradation of electrolytes, and a lithium battery using the organic electrolyte solution to improve cycle properties and life span.
2. Description of the Related Art
As portable electronic devices, such as video cameras, mobile phones, and notebook PCs, become lighter and more functional, much research has been dedicated to batteries for such devices. Particularly, because chargeable secondary lithium batteries have energy density per unit weight about 3 times higher than nickel-cadmium batteries, nickel-hydrogen batteries, nickel-zinc batteries, or the like, and rapid charging is possible, active research and development is being carried out for lithium batteries.
Conventional lithium batteries operate at a high driving voltage such that a traditional aqueous electrolyte cannot be used because the lithium anode reacts vigorously with the aqueous solution. Therefore, an organic electrolyte solution in which lithium salt is dissolved in the organic solvent is used in lithium batteries. The organic solvent used may preferably be an organic solvent with a high ion conductivity and permittivity and low viscosity. A single organic solvent satisfying all conditions is difficult to obtain, and therefore, a mixed solvent system such as a high permittivity organic solvent and a low viscosity organic solvent or the like is used.
When a polar, non-aqueous carbonate solvent is used, the anode reacts with the electrolyte in the secondary lithium battery, thereby consuming excess charge. Due to this irreversible reaction, a passivation layer, such as a solid electrolyte interface (SEI), is formed on the surface of the anode. Such an SEI prevents the electrolyte solution from degrading, thereby allowing a stable charge and discharge to be maintained. Moreover, the SEI is an ion tunnel, tunneling and solvating only lithium ions, and preventing intercalation of the organic solvents in the anodes through which the lithium ions move, thereby preventing the anode structure from collapsing.
However, as the charge and discharge of the battery is repeated at a high voltage, i.e., 4V, a rift is gradually formed in the SEI by expansion and contraction of the active materials produced by the charge/discharge process, and the SEI is eventually peeled from the electrode surface. Therefore, as shown in FIG. 1, an electrolyte is in direct contact with the active material, and electrolyte degradation continuously occurs. Once the rift is formed, the rift is continuously developed during the charge/discharge process, thereby deteriorating the active materials. As a result, an SEI made only of a polar solvent and a lithium salt cannot be maintained. Consequently, an internal resistance of the anode increases, resulting in a decrease in the battery capacity. In addition, the electrolyte content decreases due to the degradation of the organic solvent, and the electrolyte within the battery runs out making sufficient ion transfer difficult.
In order to solve the above and/or other problems, direct contact of the anode active material and the electrolyte while keeping lithium ion conductivity from decreasing is in demand so as to improve the charge/discharge properties of a lithium battery.